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## #1 2017-05-30 10:07:18

Member
Registered: 2017-02-23
Posts: 31

### [Solved] Buckling loads of a shell

Hi

So I'm continue analyzing the shell that I discussed in the post: Distribute a load to a set of nodes (Sorry I cannot post links).
Now I'm trying to do a buckling analysis wich I do with these steps:

``````# Resolution
# ----------

res1=MECA_STATIQUE(  MODELE=modl,
CHAM_MATER=chmat,
CARA_ELEM=cara,
EXCIT=(
_F( CHARGE = rdisp),
_F( CHARGE = clim),
_F( CHARGE = press),
OPTION = 'SIEF_ELGA',
);

# Stress field to calculate the geometric stiffnes matrix
# -------------------------------------------------------

stressg = CREA_CHAMP (
RESULTAT = res1,
OPERATION = 'EXTR',
TYPE_CHAM = 'ELGA_SIEF_R',
NOM_CHAM = 'SIEF_ELGA',
TYPE_MAXI = 'MINI',
TYPE_RESU = 'VALE'
)

# Elementary matrices and Assembly
# ---------------------------

matg = CALC_MATR_ELEM (OPTION = 'RIGI_GEOM',
MODELE = modl,
CARA_ELEM = cara,
SIEF_ELGA = stressg,)

matm = CALC_MATR_ELEM (OPTION = 'RIGI_MECA',
MODELE = modl,
CHAM_MATER = chmat,
CARA_ELEM = cara,
CHARGE = (rdisp, clim,
),)

nuddl = NUME_DDL (MATR_RIGI = matm,)
masrig = ASSE_MATRICE (MATR_ELEM = matg,
NUME_DDL = nuddl,)
masrim = ASSE_MATRICE (MATR_ELEM = matm,
NUME_DDL = nuddl,)

# Calculate the modes
# -------------------

modp1 = CALC_MODES (MATR_RIGI_GEOM = masrig,
OPTION = 'PLUS_PETITE',
MATR_RIGI = masrim,
SOLVEUR_MODAL  =
_F(
METHODE='SORENSEN'
),
TYPE_RESU = 'MODE_FLAMB',
CALC_CHAR_CRIT = _F(
NMAX_CHAR_CRIT = 6,
),
)``````

I get very low values for the critical load

``````numéro    charge critique    norme d'erreur
1       2.37993E-02        1.35091E-10
2       2.37993E-02        1.43175E-10
3       2.43823E-02        1.52333E-10
4       2.43823E-02        1.21724E-10
5       2.64413E-02        9.63314E-11
6       2.64413E-02        1.12501E-10 ``````

and the modes are global

As in the other post I'm comparing the results with the ones I get using abaqus, where I get much bigger critical load:

``````MODE NO      EIGENVALUE

1      0.51168
2      0.53620
3      0.54860
4      0.55567
5      0.56876
6      0.57455 ``````

and the modes are local which correspond to the location of maximun compression values, that makes more sense than the
global modes:

The rest of results (displacements, stresses...) of the linear static analysis, I get the same values in code_aster and abaqus.

What can I do to solve this?
I attach the .comm and .med file.

Thanks.

Last edited by Msegade (2017-05-31 10:47:04)

Attachments:

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## #2 2017-05-30 15:05:08

jeanpierreaubry
Guru
From: nantes (france)
Registered: 2009-03-12
Posts: 3,675

### Re: [Solved] Buckling loads of a shell

hello

what is the variable load upon which buckling is to be calculated
this is not very clear in your example

jeean pierre aubry

freely available here https://framabook.org/beginning-with-code_aster/

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## #3 2017-05-30 22:43:37

Member
Registered: 2017-02-23
Posts: 31

### Re: [Solved] Buckling loads of a shell

jeanpierreaubry wrote:

hello

what is the variable load upon which buckling is to be calculated
this is not very clear in your example

jeean pierre aubry

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## #4 2017-05-31 05:48:58

jeanpierreaubry
Guru
From: nantes (france)
Registered: 2009-03-12
Posts: 3,675

### Re: [Solved] Buckling loads of a shell

do you mean they vary linealy TOGETHER at the same rate ?

freely available here https://framabook.org/beginning-with-code_aster/

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## #5 2017-05-31 08:09:18

Member
Registered: 2017-02-23
Posts: 31

### Re: [Solved] Buckling loads of a shell

jeanpierreaubry wrote:

do you mean they vary linealy TOGETHER at the same rate ?

Yes, later I would want to make another analysis where I  just vary one of the loads while remaining the other costant,
but the results I got in abaqus are with both loads varying linealy together at the same rate.

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## #6 2017-05-31 09:09:34

jeanpierreaubry
Guru
From: nantes (france)
Registered: 2009-03-12
Posts: 3,675

### Re: [Solved] Buckling loads of a shell

i get the frist critical at 0.5465 with the shape shown attached

Attachments:

freely available here https://framabook.org/beginning-with-code_aster/

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## #7 2017-05-31 09:30:29

Member
Registered: 2017-02-23
Posts: 31

### Re: [Solved] Buckling loads of a shell

jeanpierreaubry wrote:

i get the frist critical at 0.5465 with the shape shown attached

That's what I was looking for!

Can you please share the .comm file?

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## #8 2017-05-31 09:52:14

jeanpierreaubry
Guru
From: nantes (france)
Registered: 2009-03-12
Posts: 3,675

### Re: [Solved] Buckling loads of a shell

here it is
as can see your first trial was quite out
for buckling as for may other problems code_aster looks very verbose
but can be easily fine tuned once the first .comm file has been written

Attachments:

freely available here https://framabook.org/beginning-with-code_aster/

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## #9 2017-05-31 10:46:47

Member
Registered: 2017-02-23
Posts: 31

### Re: [Solved] Buckling loads of a shell

Thanks! Now I got it working.

Is there any reason why 'PLUS_PETITE' is not working?
If I use the same .comm file and I replace

``````modp1=CALC_MODES(
TYPE_RESU='MODE_FLAMB',
OPTION='BANDE',
STOP_BANDE_VIDE='OUI',
MATR_RIGI=mascomb,
MATR_RIGI_GEOM=masrigv,
CALC_CHAR_CRIT=_F(
CHAR_CRIT=(mini,maxi,),
),
VERI_MODE=_F(
STOP_ERREUR='NON',
),
);``````

with

``````modp1=CALC_MODES(
TYPE_RESU='MODE_FLAMB',
#OPTION='BANDE',
OPTION = 'PLUS_PETITE',
STOP_BANDE_VIDE='OUI',
MATR_RIGI=mascomb,
MATR_RIGI_GEOM=masrigv,
CALC_CHAR_CRIT=_F(
#CHAR_CRIT=(mini,maxi,),
NMAX_CHAR_CRIT = 6,
),
VERI_MODE=_F(
STOP_ERREUR='NON',
),
);``````

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## #10 2017-05-31 10:57:36

jeanpierreaubry
Guru
From: nantes (france)
Registered: 2009-03-12
Posts: 3,675

### Re: [Solved] Buckling loads of a shell

Is there any reason why 'PLUS_PETITE' is not working?

this is probably explained somewhere in the doc
as the critical buckling load factor may take negative value
it will always be possible to find a value close to "minus infinity"
which will probably be meaningless

freely available here https://framabook.org/beginning-with-code_aster/

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